This invention relates to an approach to protect aircraft against threats that use infrared sensors.
Threats against military aircraft, such as air-launched or ground-launched missiles, are typically guided by a radar sensor, an infrared sensor, or both. Radar sensors are highly accurate in identifying and locating their targets. They have the disadvantage that they are active devices that emit radar signals, and their emissions may be detected by the target and used to evade or to launch a counter-attack against the radar source.
Infrared sensors, on the other hand, are passive devices that do not reveal their presence or operation. The great majority of aircraft losses to hostile attacks over the past 20 years have been to infrared-guided missiles. In most cases, the pilots of the aircraft that were shot down were not aware that they were under attack until the infrared-guided missile detonated.
Infrared-guided missiles have the disadvantage that they typically must be initially positioned much more closely to their potential targets in order for the infrared sensor of the missile to be effective, as compared with a radar-guided missile. The fields of view of the infrared sensors are usually quite narrow, on the order of a few degrees. In most cases, the infrared sensor must therefore acquire its potential target prior to launch of the missile and remain xe2x80x9clocked ontoxe2x80x9d the target for the entire time from launch until intercept. If the acquisition is lost during the flight of the missile, it is usually impossible to re-acquire the target without using an active sensor that warns the target of its presence.
There are a number of countermeasures to defeat infrared-guided missiles. Historically, the most common countermeasure has been the use of flares that produce false signals to confuse the infrared sensor. The current generation of infrared-guided missiles utilize counter-countermeasures programmed to ignore flares, based upon distinguishing features of the flares such as their different motion than the previously acquired target and/or their different heat-emitting properties as compared with the previously acquired target. Lamps and directional lasers may be used to blind or confuse the infrared sensor, but these approaches have drawbacks in respect to size, weight, complexity, and power requirements.
An important advance in infrared countermeasures to protect aircraft is described in U.S. Pat. No. 6,055,909. In the approach of the ""909 patent, discrete packets of pyrophoric or other infrared-emitting material are dispensed in a controlled manner, and ignite to produce an infrared signal. The packets may be dispensed individually or in groups, so that various decoying strategies may be employed.
The approach of the ""909 patent provides a dispensing apparatus and a dispensing strategy that are highly effective in dealing with a number of potential threats. However, there are other situations where there is a need to further improve the effectiveness of the infrared countermeasure. The present invention fulfills this need, and further provides related advantages.
The present invention provides a method for protecting an aircraft against a threat, such as a missile, that utilizes an infrared sensor. The present approach may be utilized with a towed infrared-source dispenser, or it may be used in other situations such as a dispenser built into the aircraft body, an externally mounted pod on the aircraft, or other types of dispensers. The present approach tailors the nature of the dispensed infrared sources and/or the modulated pattern of the dispensing so as to be highly effective against various types of infrared sensors and geometric engagement scenarios that may be encountered by the aircraft.
In accordance with the invention, a method for protecting an aircraft having an aircraft motion against a threat that utilizes an infrared sensor comprises the steps of providing a plurality of dispensable infrared sources in an infrared-source dispenser transported with the aircraft, wherein a set of infrared-emitting properties of the infrared sources is selected responsive to a set of infrared detecting characteristics of the infrared sensor. A modulated pattern of the infrared sources is dispensed from the infrared-source dispenser.
Typically, a rise time, a time-at-peak, and/or a burn duration of the infrared sources is selected responsive to the set of infrared detecting characteristics of the infrared sensor. The set of infrared-emitting properties may additionally be selected responsive to a set of operating characteristics of the missile and/or a set of operating characteristics of the aircraft. Thus, for example, the set of infrared-emitting properties of the infrared sources may be selected responsive to operating characteristics of the missile such as its infrared field of view of the infrared sensor or a counter-countermeasure triggering level of the infrared sensor. The set of infrared-emitting properties may for example be selected responsive to the infrared-signature characteristics of the aircraft.
In another form, a method for protecting an aircraft having an aircraft motion against a threat that utilizes an infrared sensor comprises the steps of providing a plurality of dispensable infrared sources transported in an infrared-source dispenser with the aircraft, and dispensing a modulated pattern of the infrared sources from the infrared-source dispenser. The pattern is determined responsive to a geometric engagement scenario of the aircraft and the threat and, optionally but preferably, the set of infrared detecting characteristics of the infrared sensor. The infrared performance of the dispensable infrared sources may be tailored as described previously.
The step of dispensing the modulated pattern desirably includes the substep of dispensing a first group of infrared sources including an initial-distraction subpattern having an infrared characteristic selected responsive to a set of infrared detecting characteristics of the infrared sensor, and desirably also an attention-holding subpattern tailored to the geometry of the engagement and, optionally but desirably, to the characteristics of the infrared sensor. An example of an attention-holding subpattern is a kinematic subpattern kinematically approximating the aircraft motion for a first geometric engagement scenario. The step of dispensing may further include the step of thereafter dispensing a second group of infrared sources including a second initial-distraction subpattern and a second attention-holding subpattern tailored to the characteristics of either a different engagement scenario of the same infrared sensor, or to a different infrared sensor. Typically, there is a gap between the first group of infrared sources and the second group of infrared sources.
Thus, a preferred method for protecting an aircraft having an aircraft motion against a threat that utilizes an infrared sensor comprises the steps of providing a plurality of dispensable infrared sources transported with the aircraft, wherein a set of infrared-emitting properties of the infrared sources is selected responsive to a set of infrared detecting characteristics of the infrared sensor, and dispensing a modulated pattern of the infrared sources from the aircraft determined responsive to the infrared detecting characteristics of the infrared sensor and/or a geometric engagement scenario of the aircraft and the threat.
The present approach goes beyond the approach of the ""909 patent by utilizing specific information about the nature of the threat, the nature of the protected aircraft, and the geometric engagement scenario to improve the protection of the aircraft. In many instances, intelligence information about the nature of the threat is available before the aircraft is exposed to the threat. At least some information about the type or types of missiles, the infrared sensors, and the attack strategy that are available to and used by an enemy is often known. The deployment strategies for the infrared sources discussed in the ""909 patent make use of this information in limited ways, and the present invention extends this use to the design and selection of the infrared sources themselves and the techniques for dispensing the modulated pattern of the infrared sources.
The nature of an attack by an infrared-guided missile is highly uncertain, posing a difficult protection problem for several reasons. First, the fact of an attack may not be known, because, unlike a radar-guided missile, the infrared detector emits no signal that the aircraft may detect. Second, the exact type of attacking missile may not be known with certainty. There is usually some information that an attacker will be using one or more of an inventory of several types of missiles whose characteristics vary, but exactly which one of the missiles is used in a particular attack is often not known. Third, the geometry of the engagement of the missile relative to the aircraft is not known. That is, it is not known for certain from where the missile will come relative to the flight direction of the aircraft, from where it is launched, its speed, and the like. These uncertainties are compounded by the fact that the infrared sensors of the missiles have built-in counter-countermeasures designed to defeat the countermeasures used by the aircraft.
The ""909 patent discusses some possible protection scenarios based upon the dispensing of large numbers of pyrophoric foils in controlled patterns, but does not address the issue of optimizing the nature of the pyrophoric material. The present approach utilizes the foil dispenser described in the ""909 patent or a similar type of approach, but goes further to define the nature of the pyrophoric foils that are most effective in distracting various types of infrared sensor. The present approach also goes beyond the approach of the ""909 patent to define the modulated dispensing pattern to effectively respond to a variety of threats under the highly uncertain attack conditions described in the prior paragraph. An important consideration in the modulation and dispensing analysis is the most efficient use of the pyrophoric material, so that it may be dispensed over extended periods of time in a preemptive manner.
The present approach is based upon the concept that, assuming the worst case that the sensor of the missile has already acquired the aircraft signature, it is necessary first to initially distract the sensor from the aircraft to the dispensed infrared sources, and then to hold the attention of the sensor on the infrared sources for a sufficient period of time that the sensor does not re-acquire the aircraft signature. The infrared sources fall further and further behind the aircraft as the aircraft flies away from its dispensed pattern or the dispensed pattern falls away from the aircraft. As a result, even if the counter-countermeasures capability of the missile later determines that it is pursuing a signal that is not the aircraft, it will not be possible for the sensor to re-acquire the aircraft due to the limited field of view of the missile and the movement of the aircraft.